This invention relates to a reverse-flow air conditioner, and more specifically to such air conditioner equipped with heat exchanger means particularly adapted for use during the heating cycle.
Conventional heat pumps or reverse-flow air conditioners typically comprise a compressor, four-way valve, outdoor heat exchanger, check valves, decompression devices (expansion valves or capillary tubes), receiver, indoor heat exchanger, and suction accumulator, all connected functionally by refrigerant lines.
In the existing conditioner, during the cooling operation, the hot compressed refrigerant gas delivered from the compressor flows through the four-way valve into the outdoor heat exchanger, where it condenses to a liquid as it gives up its heat to air or water. The liquid refrigerant passes through the first check valve and receiver to the second decompression device, where it is adiabatically expanded to a low-temperature, low-pressure mixture of gaseous and liquid refrigerant portions. The mixture then enters the indoor heat exchanger, where the liquid refrigerant is further gasified by heat exchange with air or water for space cooling. The gaseous refrigerant flows through the other path of the four-way valve into the suction accumulator. There it is separated from the liquid portion left unvaporized, and thus the gaseous refrigerant alone returns to the compressor.
During the heating operation, the hot compressed refrigerant gas from the compressor passes through the four-way valve into the indoor heat exchanger, and accomplishes space heating while being condensed to a liquid through the exchange of heat with air or water. The liquid refrigerant runs through the second check valve and receiver to the first decompression device. After the pressure reduction the refrigerant enters the outdoor heat exchanger, where it pumps or collects heat by exchanging heat with air or water. From the outdoor heat exchanger the refrigerant returns to the compressor via the other path of the four-way valve and the suction accumulator.
Such conventional reverse-flow air conditioners present problems as follows. When the outdoor temperature falls during the heating operation, the evaporation temperature of the refrigerant in the outdoor heat exchanger drops with a consequent decrease in the heat-pumping capacity of the refrigerant therein, allowing more unvaporized refrigerant to flow in the liquid form into the suction accumulator. Thus oversupply of the liquid refrigerant beyond the gas-liquid separation capacity of the suction accumulator will cause part of the refrigerant still in the liquid form to flow back to the compressor. This can induce liquid hammering or oil foaming, which will damage the compressor.
In an effort to prevent the return of the liquid refrigerant to the compressor during the heating operation, it has been proposed to combine the receiver and the suction accumulator in a single, integral unit so as to vaporize the liquid refrigerant in the suction accumulator with the heat transferred from the relatively hot liquid refrigerant in the receiver. The proposed arrangement has, however, proved disadvantageous because, during the cooling operation under such high-temperature conditions that the refrigerant gas in the suction accumulator is already superheated, the refrigerant gas returning to the compressor is so hot that the temperatures of the motor and bearings of the compressor rise unusually, tending to cause a trouble.
As stated, the problems common to the ordinary heat pump units for air conditioning have been that the liquid refrigerant returns to the compressor during the heating operation, and that an attempt to avoid it, in turn, results in excessive super heat of the refrigerant gas entering the compressor and hence damaging of the compressor during the cooling operation.